Biomechanical Study Of The Pull-out Force On The Pedicle Screws Of Different Transverse Angle Were Placed

The Frenchman Roy-Camille uesed the armor plate pedicle screws into inner fixation of , then pedicle screws was born. The system that fixation of pedicle screws is one of the most popular ways inner fxation in the back of spine on clinic now, it has got good fixation effects on the reduction of different spine diseases and rebuilding of spine stability. But the evulsion and letdown complication apeard on some patients. The evulsion and letdown is the most common complication of pedicle screw, it's mostly because the hold force is low, and it relates to the angle of the screw. Ensure the screw is in the pedicle, how to exert the maximal fixed function of the pedicle screw, the first thing is the angle. The anatomy of pedicle scews prove that the height is bigger its width further, and that makes the change of (SSA) have more space than the (TSA). Some correlative research show when the SSA equal to 0,the flexual moment is the smallest, so the pedicle screw is the most stable. It's easy to control the SSA, but the TSA varies according to the anchor point of the pedicle screw ,the experience of the operator and the vertebrate. The objective of the experiment is to investigate the maximal drawn force, and the maximal drawn energy when the TSA is (0degree,7degree,15degree)put into used the same type screws while the SSA and the depth of the pedicle screw is unchangeable. Used the Autograph CSS44100 Universal Testing Machine to do the exam, pedicle was pulled out with 2mm/min invariabale speed in the direction of the long axes of pedicle, and auto-memorizing machine wrote down the screws extration and migration transformation cure automaticlly. Chose fresh adult spine samples (T11～L4)and all the samples were taken X-ray inspect, and excluded obvious bone loosn, congenital abnormality, fracture and knub pathological changs. The whole process was done by one person, put the pedicle screws under the straight eyesight. The depth of it is 75%, and proved by X-ray perspective. The result show, when the TSA increase, the maximal drawn force and energy increase. the maximal drawn force of the group of 15 degree is 34.35% bigger than the group of 0 degree, the maximal drawn energuy is 25.68% bigger, while there is no obvious difference between 0 degree and 7 degree. The research of the bone structure on the pedicle screws think that the bone mineral density under the cortes of the pedicle srews is higher. The pedicle provides 60%of the total hold force to hold the screw, it is considered that it is the biggest fixation intensity when screw thread mesh inside and outside bone. In addition, many examines suggest that pedicle screws have more against drawn force. We got the result when the depth is the 75% vertebral body, when the TSA equal to 15 degree, the depth can increase. Increase 5mm will chang the maximal draw force. The depth of the screws increases the migration of drawn, then add more energy, release the extent of drawn. Extraction-migration curve shown that pedicle srews were pulled out some parts, the force of control is not fall down at once, while it is fall down slowly. This hints: The evulsion and letdown on clinic is...